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Question

How do quartz watches work?
Asked by: Tony D.

Answer

Any timekeeping device will contain at least three different parts: a drive mechanism, an escapement device (way of measuring time), and a method of display. A windup alarm clock, for example, uses a tension spring as a drive mechanism, an escapement wheel, and the gear driven mechanical hands moving across the clock face as a display of the time.

Generations of timepieces through history have worked to improve accuracy. Early mechanical clocks used falling weights as drive devices and a verge and foliot as an escapement device. The verge was a gear tensioned by a weight and the foliot was a ratchet type device that oscillated back and forth on the verge in a hold release pattern creating the familiar tick tock sound of clocks. Escapement wheels in mechanical clocks of today use much the same concept. The discovery of the pendulum by Galileo provided an even more accurate method of timekeeping as the frequency of the pendulum�s swing is not affected in time by its amplitude. In other words, even as the pendulum�s swing weakened in amplitude, the frequency between cycles remained constant.

Having a timepiece that was portable also had its challenges. Pendulum clocks don�t work well in motion. Spring driven clocks give portability, but run faster when newly wound and progressively slower as the spring relaxes. Electric clocks were an improvement, but with still relatively low frequency escapement at 60 cycles per second, were not extremely accurate.

Quartz WatchEnter the Quartz Clock. Quartz timepieces use the nature of the quartz crystal to provide a very accurate resonator which gives a constant electronic signal for timekeeping purposes. Quartz crystals are piezoelectric, which means that they generate an electrical charge when mechanical pressure is applied to them. They also vibrate if an electrical charge is applied to them. The frequency of this vibration is a function of the cut and shape of the crystal. Quartz crystals can be cut at a consistent size and shape to vibrate at thousands of times per second, making them extremely stable resonators for keeping very accurate time.

Although the piezoelectric effect of quartz crystals had been understood since the 1880s, the first application of this quartz property in the use of a time piece didn�t occur until 1927. It was in that year that the original quartz clock was invented by W.A. Marrison and J.W. Horton. Their quartz clock was a very large device as compared with today�s quartz wristwatches which also use microchip and liquid crystal display technology.

Further reading: How quartz watches work, by Horology.com
Answered by: Stephen Portz, Technology Teacher, Space Coast Middle School, FL


The basic principle behind all watches and clocks is a device that oscillates at a fixed frequency. Early mechanical watches and clocks used a pendulum or springs with some form of regulator to keep the frequency fixed. Time is simply measured by counting these oscillations. A simple device might oscillate at 1Hz (once per second), therefore 1 second would elapse for each oscillation.

Quartz watches began to appear in the early 1970s. They use a crystal of quartz (silicon dioxide) shaped like a small bar. This is a 'piezoelectric' material - when bent or compressed it generates a small electric field (and vice versa).

The crystal is formed to have a natural oscillation at around 32,000Hz. These oscillations generate small electrical signals which are 'divided down' by the circuit within the watch to the required frequency (usually seconds) and translated into pulses which are sent to the watch display or a motor to move the seconds hand.

The advantage of quartz watches is their simplicity and accuracy - crystals maintain their frequency over broad operating conditions and are cheap to make.

Higher accuracy devices generally use a material with even higher frequencies (again the frequency must be as stable as possible). Atomic clocks count the oscillations between the nucleus and the electrons in an atom (typically cesium) which oscillate at around 9 billion Hz.

There is a good website with more details of quartz watch operations at http://www.howstuffworks.com/quartz-watch2.htm
Answered by: Jules Seeley, M.S., Physics graduate; Strategy Consultant, London



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